1. Field of the Invention
The present invention relates to a magnetic head slider, and more particularly, to a magnetic head slider including a head (magnetic head)-to-medium (recording medium) spacing detecting element.
2. Description of the Related Art
In a hard disk device, a magnetic head slider on which a magnetic head is mounted is arranged facing the surface of a rotating recording medium (magnetic disk) with a space therebetween, and it performs the writing of information to the recording medium and/or the reading of information from the recording medium. In recent years, a flying height from the recording medium of the magnetic head slider is extremely small to respond higher recording density of the recording medium and is set, for example, at or below 10 nm.
In the case where the flying height of the magnetic head slider is minute, when the flying height of the magnetic head slider fluctuates for some reason, or an unexpected projection exists on the surface of the recording medium, there is the potential that the magnetic head slider is made to contact the surface of the recording medium and causes damage. For this reason, the magnetic head slider is preferably controlled so as not to contact the recording medium.
The flying height of the magnetic head slider depends on the shape (rail shape, arrangement, or the like) of an air bearing surface, the relative speed of the magnetic head slider and recording medium, and the hard disk device usage environment (pressure and temperature) or the like. In the past, the flying height of the magnetic head slider has been adjusted by optimizing mainly the shape of the air bearing surface; however, the flying height cannot be controlled during operation with this technique. Accordingly, the flying height is set to make an allowance to some extent, so that the magnetic head slider does not contact the surface of the recording medium, or the contact does not frequently occur. In contrast to this, a magnetic head slider with a built-in heater has been developed in recent years, and this enables the flying height to be controlled during operation by operating the heater to expand the air bearing surface toward the recording medium.
The latter technique is effective to reduce the flying height; however, in order to adequately control the flying height, a space between the magnetic head slider and the surface of the recording medium (head-to-medium spacing (HMS)) is preferably measurable during operation. Even with the former technique, there is an occasion that the HMS is preferably measured during operation of the hard disk device or a test device for a trial objective.
U.S. Pat. No. 7,589,928 discloses a magnetic head slider that can measure the HMS. In the magnetic head, a sensor (hereinafter, refer to as HMS detecting element) for detecting HMS is provided separately from a magnetic recording part and a reproducing part. The HMS detecting element has a metallic film formed of platinum or gold. Current flows into the HMS detecting element and a voltage drop in the HMS detecting element is measured. The voltage drop is converted to HMS by the known Wallace equation. The specification also described that the HMS detecting element is covered with a tantalum film to prevent from damage by the HMS detecting element contacting the recording medium.
In a manufacturing process of the magnetic head slider, a polishing treatment and a milling treatment are conducted to form an air bearing surface. Although these treatments may be concurrently used, the air bearing surface is ultimately formed by the milling. The milling rate differs according to the material being milled, so the air bearing surface after milling is not completely flat and minute asperity is formed. Because the HMS detecting element is positioned on the air bearing surface, it is polished together with the magnetic recording part and the reproducing part. Because the HMS detecting element is a metallic film, it is generally easy to mill and there is a greater likelihood for it to be recessed compared to other portions of the air bearing surface after milling. When this occurs, there is a greater distance between the HMS detecting element and the recording medium which presents a likelihood of reducing the sensitivity of the HMS detecting element.